High amperage molded case circuit breakers are required to interrupt large values of current extended through a plurality of downstream breakers to respective loads. Problems of course arise from the blade and contact mass required to carry the large current values and from the necessity to control the high energy arcs created on current interruption. These problems are compounded in high amperage molded case breakers since the size of the apparatus, while large, is substantially reduced from that provided in iron clad or open frame breakers.
It is customary in molded case systems breakers to provide a plurality of contacts for each current phase with each contact carried on a separate pivotable contact blade. At least one blade is considerably longer than the others and carries a large arcing contact as for example seen in U.S. Pat. Nos. 3,662,134; 4,001,742, 4,240,053 and 4,295,022.
The longer blade is usually arranged to open last in order to protect the other blade contacts against arcing and the major portion of the arc then passes through the single blade. This can lead to extensive arcs requiring considerable blade travel to extinguish and resulting in extensive contact erosion in turn requiring large expensive contacts incorporating considerable silver. In addition the manufacture of blade assemblies of different lengths is expensive.